1. Field of the Invention
The present invention relates to a method of treating fly ash for improving the properties of fly ash and a fly ash cement containing the treated fly ash.
2. Description of the Related Art
Fly ash produced as a byproduct of coal combustion in a thermal power station or the like has been conventionally popular as a material for a fly ash cement. The fly ash cement containing such fly ash requires a smaller amount of water than an ordinary Portland cement itself so as to obtain the same workability, can improve fluidity of the concrete, and can reduce water permeability. The fly ash cement has many excellent properties such that contraction during drying can be reduced, hydration heat can be reduced, and the chemical resistance can be increased. For these reasons, the fly ash cement has been widely used in dam and harbor works.
As an antipollution countermeasure, a lot of power plants employ a method of reducing the combustion temperature of powdered coal to decrease the amount of NO.sub.x generated in the power plants. For this reason, the unburned carbon contained in the fly ash is increased in amount. Therefore, when an air entraining agent generally added to the cement is added to the fly ash cement, most of the air entraining agent is adsorbed by the carbon in the fly ash. The air entraining agent cannot sufficiently achieve its function.
On the other hand, the fly ash cement is said to have a lower strength than the ordinary Portland cement itself, and the following techniques are proposed to solve this problem.
These techniques are emplified by a method of increasing the fineness of fly ash, as described in Concrete Journal 7(2), 28-37 (1969), a method of activating fly ash with an acid, as described in U.S. Pat. No. 3,953,222, and a method of curing fly ash at a high temperature, as described in J. Am. Concr. Inst., 76(4), 537-550 (1979).
The above methods, however, require pulverization energy, a post-treatment of the acid, or high-temperature curing, resulting in complicated processes. Therefore, these conventional methods are not necessarily satisfactory.